anyone out there know where i can get a schematic for turning a car wiper motor into a servo,
The SoR forum should be a good place.
First you need to define your exact needs (voltage, drive current, stall current and input signal.
Then try the search at this site, I have posted circuits for various similar purposes
the circuit basically needs control the motor through pwm. bi directional continuous rotation speed control
Do you mean like an R/C servo modified for continuous rotation?
When you modify a servo, it's not a servo anymore, as the feedback circuit which makes it a servo is surgically removed and it's turned into a gear-head motor with driver.
When you say PWM, do you mean that in the real PWM sense?
I ask this because a lot of people seems to think that an R/C servo is driven by PWM, but when you're talking real PWM (where the pulse can go from near 0% to near 100%), the circuit is different from what's used for the PPM signal used for telling servos where to go to (which is standardized to vary the M/S between the narrow range of 5% to 10% and which is a communication signal, quite unlike the PWM signals used for motor speed/power control.
If you just want to be able to drive the motor CV and CCV from a microcontroller in the easiest way, you need nothing more than an H-bridge which you feed with a PWM signal from the controller.
An H-bridge can either be made with 4 Power MOSFETS, or a DPDT relay for direction and a single MOSFET for the PWM. In both scenarios, a little "glue" (i.e. lesser components)is needed.